Ok, try this:
Uninstall Mabinogi using the Control Panel.
Then Delete all Mabinogi folders on your computer (Do a search to make sure there aren't any)
Move the installer program to your Desktop.
Reboot, and follow the other instructions from there.
After your install, make sure the game runs and then delete your installer.
Life is but a dream for the fortunate, for the rest, it's a NIGHTMARE!